Since the software Synth outputs appear in the list of available inputs for an audio track, it would seem to be simple to just record the synth onto a new audio track.  But as soon as the synth audio is selected as the input, the record enable for the track disappears! 
 
After searching help, I find "Converting your soft synth tracks to audio".  This is a 9 step procedure involving "bounce to track" and lots of fiddling around with settings. Compared to "select input source, enable record" that seems like going around the block.  To add insult, it doesn't work! Following the procedure results in nothing recorded to the destination track.
 
Can anyone explain why the obvious, straightforward method for recording audio from a soft synth is prevented from being used? That is exactly what I do to record an external synth. Why is a soft synth any different?
 
Does anyone know of an alternate (working) procedure to record the synth audio?  I don't see any way to route a bus back to a track input. I suppose I could play the SW synth through a pair of channels on my audio interface, and loop it back into Sonar on different channels, but that seems silly. What am I missing?
 

If the midi controlling the synth is already recorded you can freeze the synth and get audio.
You can bounce out the synth to your desktop (or wherever) and drag it back in Sonar. It takes seconds to do that - I did it loads of times yesterday.
I'm not 100% on this one but I seem to remember a video showing a "normal time" bounce to an external location that involved actually playing the synth in real time.

Grum.

You do not need to manually route audio track for soft synth. Recording midi from soft synth (via insert soft synth) is usually all you need as you have the flexibility to edit the midi, without having to re-do the audio.
 
If you need separate audio, follow as what Grum said.

It's different in DAW land, you don't route the output and record enable, etc. You bounce instead.
Once I'm satisfied with a soft synth track (automation, notes, velocity, sound, etc) I bounce it so I can hear how it sits in the mix and apply audio effects.
It's easy to do the conversion:
1. Select the instrument track or the midi and synth tracks.
2. Set your from and to selection points.
3. Bounce to tracks.
Done.
The whole process usually takes less than 30 seconds if you use fast bounce. Once you've got the levels set on the synth track, doing another bounce to fix something is just as fast and doesn't mess up your mix.
I've tried but don't really care for using FX on instrument tracks but that's just personal preference.
 

timg11
 What am I missing?
 

 
You're not missing anything.  This functionality does not exist in Sonar.

The Grumbleweed
bounce out the synth to your desktop (or wherever) and drag it back in Sonar.

I'm not sure what you mean by "bounce to desktop", but I played around with the bounce to tracks method more and finally got it to work. I discovered these facts:
 
1) You have to uncheck Fast Bounce (checked by default), and check Audible Bounce.  This is not mentioned in the 9-step procedure in the help file.
2) Presets don't fully "preset". They save some settings but not others. Notably, the Destination track and the Source Buses/Tracks are not part of the preset, and your settings are not remembered, even between sequential uses in the same project. They have to be manually set every time.
 
I still don't understand why the direct recording of the synth is not allowed.
 

Ad 1) that's not true, although some synths don't play nice with a fast bounce.

Is it not an option for you to use the freeze button? It's super quick and you can move the audio to a new track if you have to (I think, I almost never need this).

Recording from a synth would need to be a real-time process. Bouncing is much faster, and Fast Bounce is the preferred option, especially with X3. Not quite sure why it didn't work for you, although the most common problem people experience is not selecting the instrument's audio track and MIDI track. Don't know if you're using a simple instrument track, but I prefer a full-blown instrument setup with folder, audio, and MIDI tracks.
 
Regarding
 

Presets don't fully 'preset'. They save some settings but not others. Notably, the Destination track and the Source Buses/Tracks are not part of the preset, and your settings are not remembered, even between sequential uses in the same project. They have to be manually set every time.

 
For what sounds like your intended application most people would use Track Freeze. Bouncing is a less common event that's usually applied to a single track or group of tracks, and generally not done consecutively. Most of the time you don't need to change more than one or two defaults (if that).
 
Hope this helps.

Recently I froze a Rapture synth track but the resulting stereo audio track didn't include the panning effect. After experimenting I found that the bounce preset option "what you here" created the audio file as I needed it.  

rcklln
Recently I froze a Rapture synth track but the resulting stereo audio track didn't include the panning effect.

Right-click the freeze button and make sure "Track FX" is checked.